Although ethnio screeners are valuable in UX research recruitment to companies and sites of any size- about 10,000 visitors per day is a realistic number for successful live recruitment. When we did research at Bolt | Peters, we said six qualified recruits per hour was the minimum for effective live recruiting (you’ll get some voicemails, a few folks unwilling to participate, etc.). It's important to realize that this isn't just six responses per hour, but six recruits who meet your testing criteria. We also look for a response rate of 1.8% to see if a screener is working. Putting those together, your screener needs about 400 views an hour for true live recruiting to work. Of course, you can still do a mix of live and scheduled users with fewer views per hour.
The amount of traffic on your site can vary especially if you're planning on scheduling participants to be interviewed at a later time or are using a third party tool to gather user feedback.